
	Where results make sense

Topic: Cycloaddition

Related Topics

Sigmatropic reaction

In the News (Thu 16 Feb 12)

EXECUTIVE POWER

Iran

ANALYSIS

Pakistan

Family compact

	Pericyclic Reaction Chemistry
		Cycloaddition and the reverse process, retrocycloaddion, can be observed in the reaction between 1,3-butadiene and ethene to give cyclohexene.
		Cycloaddition is popular in the synthetic methodology when attempting to make natural products and pharmaceutical agents with involved stereochemistry because the reaction can determine the relative configuration of up to four chiral centres in a single reaction.
		The FMO argument is that the LUMO and the HOMO of ethene are phase mismatched and cycloaddition is symmetry forbidden.
	www.meta-synthesis.com /webbook/49_pericyclic/pericyclic.html (1568 words)

	Non-ionic Chemical Reactions (Site not responding. Last check: 2007-10-19)
		The reverse of a cycloaddition is called cycloreversion and proceeds by a ring cleavage and conversion of two sigma-bonds to two pi-bonds.
		The most common cycloaddition reaction is the [4+2] cyclization known as the Diels-Alder reaction.
		The common [4+2] cycloaddition known as the Diels-Alder reaction proceeds stereospecifically in a suprafacial fashion, but the [14+2] cycloaddition in equation 3 is antarafacial with respect to the polyene.
	www.cem.msu.edu /~reusch/VirtualText4/pericycl.htm (4865 words)

	V.P.Ananikov, "Ab initio study of the [4+2] cycloaddition reactions" (Site not responding. Last check: 2007-10-19)
		The cycloaddition step leading to six-membered ring allene was found to be the key stage of the process.
		Besides the first cycloaddition step, 1,2-H shifts of Pathway II are also sensitive to the presence of substituents.
		Thus, the main differences between intermolecular and intramolecular reactions are: lower barriers of the cycloaddition and the first 1,2-hydrogen shift stages due to activation entropy contribution and alkyl ring stabilization effects.
	nmr.ioc.ac.ru /Staff/AnanikovVP/ECCC7.2 (958 words)

	Asymmetric 1,3-Dipolar Cycloaddition
		The achievement of a catalytic 1,3-dipolar cycloaddition of a nitrile oxide was rather difficult because the reagent is usually too unstable to be isolated and must be generated in situ.
		The 1,3-dipolar cycloaddition of nitrile oxide using a catalytic amount (0.2 molar amount) of (R,R)-DIPT was examined with special attention directed to the order of addition and the molar ratio of the reagents.
		The catalytic asymmetric 1,3-dipolar cycloaddition of nitrone 4 to an achiral allyl alcohol (1) also proceeded enantioselectively when a catalytic amount of (R,R)-DIPT was used as a chiral auxiliary to afford cis-isoxazolidine 5 in good optical yield.
	pages.unibas.ch /mdpi/ecsoc-4/a0016/a0016.htm (923 words)

	Examples Of Cycloaddition/Elimination Reactions
		Many 2+2 cycloadditions are thought to proceed in this manner, especially in more polar solvents which stabilise the intermediate zwitterions.
		Diels Alder cycloaddition gives the final product (note how in this transition state, one of the forming C-C bonds forms at a significantly faster rate than the other, it being "tethered" by the adjacent five membered ring, whilst the other end is more floppy).
		cycloaddition, again following a 4n+2 rule of Möbius aromaticity and maintaining an axis of symmetry.
	www.ch.ic.ac.uk /local/organic/pericyclic/p1_cyclo.html (1076 words)

	Synthesis of Heterocycles Using Tandem Cyclization Processes
		In the realm of synthesis in which a premium is put on the rapid construction of polyfunctional, highly bridged carbon and heteroatom networks, the [4+2]-cycloaddition has emerged as one of the foremost synthetic methods [2].
		Cycloaddition of the initially formed dipole across the pendant indole pi-system [11] would be expected to result in the simultaneous generation of the CD-rings of the aspidosperma skeleton [12].
		The intramolecular cycloaddition behavior of the incipient isobenzofurans in response to the presence of a C=O group is striking.
	pages.unibas.ch /mdpi/ecsoc-3/a0019/a0019 (2262 words)

	IngentaConnect The mechanism of 1,3-dipolar cycloaddition reactions of cycloprop... (Site not responding. Last check: 2007-10-19)
		IngentaConnect The mechanism of 1,3-dipolar cycloaddition reactions of cycloprop...
		The mechanism of 1,3-dipolar cycloaddition reactions of cyclopropanes and nitrones — A theoretical study
		On a trouvé que les liaisons σ tendues du cyclopropane jouent le rôle d'un alcène dans une cycloaddition dipolaire [3+2] conventionnelle.
	www.ingentaconnect.com /content/nrc/cjc/2005/00000083/00000010/art00005 (558 words)

	Non-ionic Chemical Reactions
		The number of participating π-electrons in each component is given in brackets preceding the name, and the reorganization of electrons may be depicted by a cycle of curved arrows - each representing the movement of a pair of electrons.
		Cycloaddition reactions and sigmatropic rearrangements both involve pairs of σ-bond-making events (or a coupled bond-making & bond-breaking) associated with a π-electron system.
		Although cycloaddition reactions are concerted (no intermediate species are formed), the two new bonds are not necessarily formed in a synchronous fashion.
	www.cem.msu.edu /~reusch/VirtualText/pericycl.htm (5181 words)

	[No title] (Site not responding. Last check: 2007-10-19)
		In a [4+2] cycloaddition reaction, new bonds will form between the terminal carbons of the diene and the alkene carbons of the dienophile, as shown below.
		In a [4+2] cycloaddition reaction, new bonds will form between the terminal carbons of the diene and the alkene carbons of the dienophile.
		To identify the reactants in a [4+2] cycloaddition reaction, identify the carbons of the dienophile (they will be the two carbons in a six-member ring which are opposite to the double bond in the product) and mentally split the bonds, separating the carbon skeletons of the diene and the dienophile.
	www.chem.uic.edu /web1/OCOL-II/WIN/CH14/15B/15BANS.HTM (320 words)

	Cycloaddition - Wikipedia, the free encyclopedia
		Cycloadditions are usually described by the backbone size of the participants.
		Cycloadditions in which 4n π electrons participate can also occur as a result of photochemical activation.
		In the (i+j+...) cycloaddition notation i and j refer to the number of atoms involved in the cycloaddition.
	en.wikipedia.org /wiki/Cycloaddition_reaction (428 words)

	Shea Research Group (Site not responding. Last check: 2007-10-19)
		Efforts have focused on cycloaddition chemistry, more specifically the development of the type 2 intramolecular Diels-Alder reaction.
		We have exploited the intrinsic stereo- and regiochemical bias of the cycloaddition for the synthesis of highly substituted carbocyclic and heterocyclic rings.
		We are studying the scope and mechanism of this reaction as well as developing additional asymmetric catalysts for the type 2 IMDA.
	chem.ps.uci.edu /~kjshea/research/synthmethod.htm (306 words)

	IngentaConnect 1,3-Dipolar cycloaddition reactions in heterocyclic synthesis. Sy... (Site not responding. Last check: 2007-10-19)
		Cycloaddition of 3-(4-acetylphenyl)sydnone (1) with DMAD gave dimethyl 1-(4-acetylphenyl)-1H-pyrazole-3,4-dicarboxylate (2), which on bromination yielded the corresponding monobromoacetyl (3) and dibromoacetyl (4) derivatives.
		Both compounds 3 and 4 on reaction with thiourea and thioacetamide afforded the 2-amino- (5) and the 2-methyl- (6) thiazole derivatives respectively, while compound 3 on reaction with 2-aminothiazole gave the imidazothiazole 7.
		Compound 3 was converted into its azide (8), which on 1,3-dipolar cycloaddition with DMAD afforded the 1,2,3-triazole-4,5-dicarboxylate (9).
	www.ingentaconnect.com /content/stl/jcr/2005/00002005/00000009/art00016 (139 words)

	Rigby Group Publications
		Rigby, J. H.; Cavezza, A.; Heeg, M. "Asymmetric Induction in [1+4] cycloadditions of vinyl isocyanates with chiral nucleophilic carbenes" Tetrahedron Lett.
		Rigby, J. "Chromium(0)-promoted higher-order cycloaddition reactions in organic synthesis" Tetrahedron 1999, 55, 4521-4538.
		Rigby, J. H.; Chouraqui, G. "First [6+4] cycloaddition of tropone and a furan moiety: Rapid entry into a highly functionalized ingenane skeleton" Synlett 2005, 16, 2501-2503.
	chem.wayne.edu /rigby/publications.html (2244 words)

	Danheiser Group - Methodology - Cycloadditions of Highly Unsaturated, Conjugated Molecules
		The general goal of our work in this area is the design of cycloaddition processes which, like cycloaromatizations, involve highly unsaturated conjugated molecules and proceed via strained and/or high energy intermediates to produce new aromatic and dihydroaromatic rings.
		We have shown that the intramolecular [4+2] cycloaddition of conjugated enynes with alkynes and alkenes provides a powerful method for the synthesis of aromatic and dihydroaromatic compounds.
		[4 + 2] Cycloaddition of Conjugated Enynes and Heteroenynes
	web.mit.edu /chemistry/rld/methods/unsaturated.html (229 words)

	Orbital Symmetry in Cycloaddition Reactions (Site not responding. Last check: 2007-10-19)
		Cycloaddition reactions are extremely vital in organic syntheis work.
		The Diels-Alder is sometimes called a [4+2] cycloaddition, indicating a hydrocarbon of four carbons combines with one of two carbons.
		Below is a diagram showing the HOMO of 1,3-butadiene and the LUMO of ethylene approach each other, forming the Diels-Alder transition state.
	user.mc.net /~buckeroo/OSCR.html (200 words)

	Wiley::Synthetic Applications of 1,3-Dipolar Cycloaddition Chemistry Toward Heterocycles and Natural Products
		Dipolar cycloaddition chemistry has found many useful synthetic applications, particularly with respect to the preparation of compounds with new chiral centers.
		Beyond the ability of the 1,3-dipolar cycloaddition reaction to produce heterocycles, its importance extends to two other areas of organic synthesis, both of which are included in the current volume.
		Second, many 1,3-dipolar cycloadditions have the ability to generate rings (and the functionality derived from transformations of such rings) containing several contiguous stereocenters in one synthetic operation.
	www.wiley.com /WileyCDA/WileyTitle/productCd-0471280615.html (288 words)

	Cycloaddition − Wikipedia
		Die Cycloaddition ist eine chemische Reaktion der organischen Chemie.
		Die Cycloaddition ist ein Spezialfall der Pericyclischen Reaktionen.
		Der bekannteste und häufigste Spezialfall der Cycloaddition ist die [4+2]-Cycloaddition, darunter fällt auch die Diels-Alder-Reaktion.
	de.wikipedia.org /wiki/Cycloaddition (304 words)

	V.P.Ananikov "Theoretical study of tandem cycloaddition and fragmentation reactions" (Site not responding. Last check: 2007-10-19)
		The intramolecular alkyne and CC-CH=X units may undergo either [4+2] or [3+2] cycloaddition pathways depending on the nature of X. Involving enynes (X=CH) as substrates results in [4+2] cycloaddition reaction while in the case of heteroatom substituted molecules (X=O, S, NH) the energetically favored pathway starts with [3+2] cycloaddition.
		Whereas 1,2-C shift and [3+2] cycloaddition are unlikely due to high activation energies calculated for the 4-TS and 8-TS.
		Analyzing both MP2 and B3LYP energy surfaces the same conclusions can be drawn: 1) for heteroatom-containing molecules the [3+2] cycloaddition pathway is preferred over the sequence of [4+2] cycloaddition and 1,2-C shift; 2) for the enynes both [3+2] cycloaddition and 1,2-C sift are rather unlikely.
	nmr.ioc.ac.ru /Staff/AnanikovVP/ECCC9 (852 words)

	Intramolecular [2 + 2] cycloaddition imine-ketenimine
		The addition of different nucleophiles to the central sp carbon and the cycloaddition reactions to produce heterocyclic compounds have received considerable attention in the literature dealing with ketenimines.
		Concerning their cycloaddition reactions, just two papers describing briefly the intermolecular cycloaddition of ketenimines with imines have been reported.
		The intramolecular cycloaddition was notably accelerated by heating, and we could not isolate from the reaction mixture the expected C1-trimethylsilyl
	www.ch.ic.ac.uk /ectoc/echet96/papers/022/index.htm (736 words)

	Photon-assisted cycloaddition
		We have seen that the thermal cycloaddition of two ethenes is “forbidden” because the energy of the reactants goes up significantly as the reactants (two ethenes) approach each other.
		We reach this conclusion through the use of the correlation diagram, which correlates or joins up orbitals of the reactants and products which have the same symmetry.
		It is possible to do this by exciting the electrons in the reactants using UV light.
	www.chm.bris.ac.uk /pt/ajm/sb04/L4_p10.htm (126 words)

	Synthesis of quinoline derivatives by [4+2] cycloaddition reaction
		Synthesis of quinoline derivatives by [4+2] cycloaddition reaction
		Recently, we have reported the synthesis of quinoline ring system by an intermolecular [4+2] cycloaddition of the Schiff base as a diene with the styrene derivative as a dienophile.
		It is thus of interest to examine the further application of the above cycloaddition employing cyclic enol ether as a dienophile to construct a fused quinoline ring system, not only for investigation of its extension, but also because of the occurrence of a number of physiologically interesting quinoline alkaloids as natural products.
	www.combichemistry.com /chemistry-articles/quinoline.html (110 words)

	Cycloaddition reactions
		Why is is that cis-1,3-butadiene and ethene react to form cyclohexene when heated:
		but the analogous cycloaddition of two ethene molecules does not work?
		(2+2 cycloaddition, calculated to be exothermic by 75 kJ/mol)
	www.chm.bris.ac.uk /pt/ajm/html/L5_p1.htm (47 words)

	Quantum Chemical Characterization of Cycloaddition Reactions between the Hydroxyallyl Cation and Dienes of Varying ... (Site not responding. Last check: 2007-10-19)
		Hydroxyallyl cation prefers to undergo cycloaddition reactions with dienes in a stepwise fashion.
		Analysis of positive charge distribution in the intermediate formed after initial C-C bond formation provides a simple unifying method for rationalizing changes in reactivity as a function of diene nucleophilicity.
		Interestingly, for the initial intermediate generated from 1,3-butadiene, [3+2] cycloaddition reactions are favored, but closure to form a C-O bond as the second step results in an intermediate that can undergo a low-energy Claisen rearrangement to form a 7-membered ring product identical to that expected from compact [4+3] cycloaddition.
	pollux.chem.umn.edu /publications/abstract105.html (157 words)

	[No title]
		This experiment demonstrates the remarkable synthetic utility of cycloaddition reactions, which are important because they involve the formation of two C-C bonds in a single chemical step, and usually proceed with a high degree of (predictable) stereospecificity and regiospecificity.
		H nmr spectra to those of the initial adduct.
		Would you expect it to undergo intramolecular photochemical [2+2] cycloaddition like the original adduct?
	www.chemistry.mcmaster.ca /courses/3d03/old-labmanual/3d3ex6.html (1449 words)

Try your search on: Qwika (all wikis)